It is already state of the art (Erich Hau, “Windkraftanlagen” (“Wind Power Installations”), 1996, 2nd edition, page 113 ff) for a rotor blade which is optimized for a maximum degree of efficiency to be provided in the inner region with very great blade depths. (See FIG. 1.) Such rotor blades are used for example by Enercon in the wind power installation of type E-40 (power range is between 500 and 600 KW). The inner region of a rotor blade is in that respect that portion which is close to the hub (rotor blade root) and accordingly involves a small radius.
While such a rotor blade which is optimised for a maximum degree of efficiency is good to produce for relatively small installations and can also be transported without any problem, such a rotor blade design suffers from two disadvantages. Firstly, the very large area of the rotor blade at the rotor blade root gives rise to very high loads when high wind speeds are involved. The wind power installation is usually then already shut down. However, the entire wind power installation has to be designed (dimensioned) for those very high loads. The second disadvantage lies in production of a rotor blade involving a very great blade depth. While that disadvantage is still scarcely significant in relation to rotor blades of a relatively small radius, manufacture and subsequent transportation of such a rotor blade which is of a very great length (for example more than 50 m) is highly complicated and in part impossible and the very great blade depth entails an extremely great increase in material and labour.
For those reasons the proposal has been made to circumvent the great blade depths. FIG. 2 shows a design configuration which was earlier frequently built in Denmark.
In this embodiment of a rotor blade, the inner region was completely eliminated. As the harvest area corresponds to the rotor area which is swept, it was assumed that it was possible to forego that very small area (inner region area) which only corresponds to about 5% of the total area, or to slightly enlarge the rotor diameter in order thereby to compensate for the area flow.
In that respect however the point was overlooked or not noted that this results in the formation of an aerodynamic hole in the near region of the wind power installation with rotor blades as shown in FIG. 2. In the near region the wind can flow unimpededly through that hole without experiencing any resistance. The result of this is that no laminar flow is built up in the inner region (first region of the rotor of the wind power installation) of the beginning profile at the rotor blade. That also means that the first region of the rotor blade with an (active) rotor profiling cannot contribute to energy generation.
Enercon already developed at a very early date (about 1990) thick, cut-off profiles in order to get around the above-indicated problems.
FIG. 3 shows such a profile which was used in the inner region of the rotor blade. In the case of large wind power installations (rotor diameters of over 70 m) however even the cut-off profiles result in blade depths of up to 6 m, which makes transportation of such rotor blades extremely difficult and makes the manufacture thereof extraordinarily complicated and expensive.